The purpose of this study is to identify treatments to prevent or slow the rate of progression of renal disease in non-insulin-dependent diabetes mellitus (NIDDM) in the Pima Indians. The efficacy of the angiotensin-converting-enzyme inhibitor (ACEi) lisinopril is being tested in 20 Pima Indians with overt diabetic kidney disease. Glomerular function was measured in each subject for about 4 years prior to treatment with lisinopril and its will be measured at 6-monthly intervals during treatment. Changes in glomerular function before and after initiation of lisinopril treatment will be examined. A randomized, double-blind, placebo-controlled clinical trial is being conducted in 200 diabetic Pima Indians with normal urinary albumin excretion or early microalbuminuria to determine whether blockade of the angiotensin II receptor with losartan will prevent or attenuate the development and progression of early diabetic nephropathy. Masked treatment with drug or placebo will be converted to active treatment in those who develop overt nephropathy during treatment. Kidney biopsies will be performed after five years in 60 subjects who initially had microalbuminuria. Subjects for biopsy will be selected equally from the drug and placebo groups. Morphometric analyses will be used to identify any structural differences between the treatment groups. Treatment will continue until subjects reach the primary endpoint of a doubling of serum creatinine concentration or until there is sufficient evidence to draw conclusions regarding the renoprotective efficacy of losartan.